The present invention has for its object a total field imaging probe enabling logs to be made over the whole periphery of the wall of a hole excavated in the sub-soil.
The technical sector of the invention is the manufacture and exploitation in situ of tools or probes for making measurements of the characteristics of the soil in a bore-hole traversing geological formations and for remotely reading and analyzing these measurements.
One of the principal applications of the invention is the use thereof for effecting imaging logs of wells making it possible to obtain a good coverage of the whole of the excavation, using different conventional individual measuring means, such as acoustic or microresistive measurements.
In fact, different systems and processes are known, of which certain have formed the subject matter of Patent Applications and which relate to the same object and/or the same application as the present invention, but of which the technical solutions retained do not allow good performances and/or are difficult to implement.
In the following description and by way of definition, the generic term "electrical logging" or "log" designates the continuous recording of physical parameters of the formations encountered during excavation, as a function of the depth.
It will firstly be recalled that imaging logging is a novel concept making it possible, from conventional individual measurements, to present along an evolute of the wall of the borehole as a function of the depth, the response of this wall to a physical measurement, such measurement having a vertical and horizontal definition of the order of several tens of centimeters for usual logs.
This representation, on any displayable visual support and, furthermore, oriented in space, therefore constitutes an artificial image of the formations encountered.
Implementation thereof essentially necessitates:
an investigation with the aid of the parameter measured, allowing the maximum coverage of the wall of the well;
means for locating in space;
a processing of each measurement representing the amplitude of this parameter in the form of a colour or a gradual range of greys; for example, the high resistivities in white and the very low in black. The amplitude of a sound wave, emitted by a sensor, after reflection by the wall of the well, may be processed in the same manner.